Kinetics of 5α-Cholestan-3β-ylN-(2-Naphthyl)carbamate/n-Alkane Organogel Formation and Its Influence on the Fibrillar Networks

Abstract

The kinetics and mode of nucleation and growth of fibers by 5alpha-cholestan-3beta-yl N-(2-naphthyl)carbamate (CNC), a low-molecular-mass organogelator (LMOG), in n-octane and n-dodecane have been investigated as their sols were transformed isothermally to organogels. The kinetics has been followed in detail by circular dichroism, fluorescence, small-angle neutron scattering, and rheological methods. When treated according to Avrami theory, kinetic data from the four methods are self-consistent and describe a gelation process involving one-dimensional growth and "instantaneous nucleation". As expected from this growth model, polarized optical micrographs of the self-assembled fibrillar networks (SAFINs) show fibrous aggregates. However, their size and appearance change abruptly from spherulitic to rodlike as temperature is increased. This morphological change is attended by corresponding excursions in static and kinetic CD, fluorescence and rheological data. Furthermore, the rheological measurements reveal an unusual linear increase in viscoelastic moduli in the initial stages of self-assembly. Each of the methods employed becomes sensitive to changes of the system at different stages of the transformation from single molecules of the LMOG to their eventual SAFINs. This study also provides a methodology for investigating aggregation phenomena of some other self-assembling systems, including those of biological and physiological importance.

Structural and Thermal Properties of Unpurified and Purified 12-Hydroxystearic Acid Solutions

“…They form a three-dimensional network of crystalline fibers in an organic solvent and cause gelation [1,2]. The phase behavior of the sol-gel transition in the gelator/solvent systems depends on the melting behavior of the crystallites, and the sol-gel transitions exhibit thermally reversible behavior [3]. The fiber diameter usually ranges from nanometers to micrometers and therefore there exist many interfaces between the fiber and the solution in organogels [4,5].…”

Hunter's Oligoamide: A Functional C2‐Symmetric Molecule with Unusual Topology for Selective Organic Gel Formation

“…[8] Organogels can increase the viscosity of the medium by a factor of 10 10 , trap up to 10 5 liquid molecules per gelator, and can be sensitive to a variety of stimuli. [9] Generally, the gelled state can be seen as a metastable state between liquid and solid.…”

Engineering of Small Molecule Organogels by Design of the Nanometer Structure of Fiber Networks

“…It has been verified that network formation in many smallmolecule organogels is a process that consists of the primary nucleation of the gelators and the subsequent growth of the fibers (nucleation-growth process). [13][14][15][16] On the basis of this mechanism, a permanent and strong 3D fiber network can only be formed when branching occurs at the tips or the side faces of growing fibers. This is called "crystallographic mismatch branching (CMB)".…”